1. Field of the Invention
This invention relates to a lathe machine, more particularly to a lathe machine adapted for processing a deep internal bore in a workpiece.
2. Description of the Related Art
Referring to FIG. 1, a conventional lathe machine 10 for internal bore processing as disclosed in Taiwan Publication No. 200940219 is shown to include a headstock 11, a turret 12, and a tailstock 13. The headstock 11 is fixedly mounted on a machine bed (not shown) for rotatably holding a workpiece 100. The turret 12 includes a saddle 121 movably disposed on the machine bed along a Z-axis direction, and a rotatable turret mount 122 movably disposed on the saddle 121 along an X-axis direction for mounting a plurality of cutting tools (not shown). The tailstock 13 includes a bottom seat 131 movably disposed on the machine bed along the Z-axis direction, a tailstock mount 132 movably disposed on the bottom seat 131 along the X-axis direction, and a centering mandrel 133 and a drilling tool holder 134 which are disposed on the tailstock mount 132 and which are juxtaposed to each other. A first plug 124 and a first socket 135 are disposed on the saddle 121 and the bottom seat 131, respectively, and are engageable with each other such that the tailstock 13 is driven by the saddle 121 to move in the Z-axis direction. A second plug 125 and a second socket 136 are disposed on the turret mount 122 and the tailstock mount 132, respectively, and are engageable with each other such that the tailstock mount 132 is driven by the turret mount 122 to move in the X-axis direction. A selected one of the centering mandrel 133 and the drilling tool holder 134 is used according to the machining process to be performed. When it is desired to use the centering mandrel 133, the tailstock mount 132 is displaced in the X-axis direction to bring the centering mandrel 133 in line with a spindle axis of the workpiece 100. Then, a positioning member (not shown) disposed on the bottom seat 131 is driven to secure the tailstock mount 132 in place. When it is desired to perform a deep internal boring, the saddle 121 is engaged with the bottom seat 131 so as to control the amount of movement of a drilling tool mounted on the drilling tool holder 134 in the X-axis direction.
However, as the saddle 121 is engaged with the bottom seat 131 only by means of the first plug 124 and the first socket 135, the first plug 124 and the first socket 135 have to bear the weight of the entire tailstock 13, so that shaking and intermittent separation of the saddle 121 and the bottom seat 131 may occur during machining processes. Moreover, it is difficult to displace the centering mandrel 133 to be precisely in line with the spindle axis of a workpiece 100, thereby adversely affecting the centering effect.